Write about Thorium atom.

     

Thorium is a weakly radioactive metallic chemical element with the symbol Th and atomic number 90.  Thorium is silvery and tarnishes black when it is exposed to air, forming thorium dioxide;  it is moderately hard, malleable, and has a high melting point Thorium is an electropositive actinide whose chemistry is an electropositive actinide whose chemistry is dominated by the +4 oxidation state;  it is quite reactive and can ignite in air when finely divided.

     All known thorium isotopes are unstable.  The most stable isotope, 232Th has a half-life of 14.05 billion years, or about the age of the universe; it decays very slowly via alpha decay, starting a decay chain named the thorium series that ends at stable 208Pb.  On Earth, thorium, bismuth, and uranium are the only three radioactive elements that still occur naturally in large quantities  as primordial elements.  It is estimated to be over three times as abundant as uranium in the Earth's crust, and is chiefly refined from monazite sand as a by-product of extracting rare-earth metals.

     Thorium is still being used as an alloying element in TLG welding electrodes but is slowly being replaced in the field with different compositions in the field with different compositions.  It was also material in high-end optics and scientific instrumentation, used in some broadcast vacuum tubes, and as the light source in gas mantles, but these uses have become marginal.  It has been suggested as a replacement for uranium as nuclear fuel in nuclear reactors, and several thorium reactors have been built.  thorium is also used to strengthen magnesium, coating tungsten wire in electrical equipment, controlling the grain size of tungsten in electric lamps, high-temperature crucibles, in glasses and used in camera and scientific instrument lenses.  Other uses for thorium include heat-resistant ceramics, aircraft engines, and in light bulbs.